This invention relates to a parallel plate heat exchanger for cooling large transformers.
Referring to FIGS. 1-3 which illustrate a conventional heat exchanger, a heat generating unit 1 such as a transformer is mounted within an enclosure or housing 2 having a sidewall 2a. The heat exchanger 3 comprises parallel metallic plates 5, plenums 8 and connecting tubes 9. The plates 5 are each formed by overlying a pair of plates 51 as shown in FIG. 2, welding along lines 6, and expanding the space between the plates 51 with compressed air. Openings 7 are provided at the top and bottom of each plate. The enclosure 2, the plenums 8, the tubes 9 and the plates 5 are filled with a heat conveying fluid 4. The adjacent folded ends 5a of the plates 5 are welded together to form the parallel plate unit.
The plenums 8 communicate with the openings 7, and the tubes 9 communicate between the interior of the housing 2 and the plenums at the top and bottom of the sidewall 2a. Heat generated by the unit is dissipated through the plates 5 in a well known manner by the convection flow of the fluid 4 through the upper tube 9, the upper plenum 8, the plates 5, the lower plenum 8, and back through the lower tube 9 into the housing 2.
In such a conventional heat exchanger the cooling efficiency is reduced by the low fluid flow velocity due to the relatively large resistance and complex flow path defined by the plenums 8 and tubes 9.
The length L of each plate 5 must be at least twice the diameter D of the tubes 9 or the height D of the plenums 8, but shorter than the height H of the enclosure 2. The radiating surface S of the heat exchanger 3 may be expressed as S=nwL, where n, w and L indicate the number of plates 5, the width of each plate and the length of each plate 5, respectively. The width w or the number n of plates must thus increase, and attendantly the mass of the heat exchanger, as the length of the plates decreases.
In stamping out the plates 51 from blanks 11 (FIG. 3), the four corners 10 are discarded, and this increases the cost of the heat exchanger. Further, when the heated air rises up between the plates 5, its smooth flow path is disturbed by the obstacles represented by the plenums and tubes, and this lowers the cooling efficiency and capacity of the unit.